JSON Schema support documentation

.gitignore

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 # Dependencies and AdonisJS build
 node_modules
 build
+package-lock.json
 
 # Secrets
 .env

.npmrc

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+package-lock=false

content/docs/db.json

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     "contentPath": "./guides/helpers.md",
     "category": "Guides"
   },
+  {
+    "permalink": "json_schema",
+    "title": "JSON Schema",
+    "contentPath": "./guides/json_schema.md",
+    "category": "Guides"
+  },
   {
     "permalink": "types/string",
     "title": "String",

content/docs/guides/json_schema.md

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+---
+summary: Convert Vine Schema to JSON Schema
+---
+
+# JSON Schema
+
+[JSON Schema](https://json-schema.org/) is a standard for describing the structure of JSON with JSON. It's widely used in [OpenAPI](https://www.openapis.org/) definitions and defining [structured outputs](https://platform.openai.com/docs/guides/structured-outputs?api-mode=chat) for AI.
+
+With VineJS you can **convert Vine schemas into JSON Schemas** using the `toJSONSchema` method.
+
+```ts
+import vine from '@vinejs/vine'
+
+const schema = vine.create(vine.object({
+  firstName: vine.string().optional(),
+  lastName: vine.string().optional(),
+  email: vine.string().email(),
+}))
+
+schema.toJSONSchema()
+// => {
+//   type: 'object',
+//   properties: { 
+//     firstName: { type: 'string' }, 
+//     lastName: { type: 'string' } 
+//     email: { type: 'string', format: 'email' } 
+//   },
+//   required: [ 'email' ],
+//   additionalProperties: false,
+// }
+```
+
+:::warning
+
+JSON Schema cannot represent all complex schemas that VineJS can create. We always try to find the closest equivalent, otherwise we represent it as an `Any` type.
+
+:::
+
+## Customize Schema
+
+You can customize the computed JSON schema by using the `meta` modifier.
+
+```ts
+vine.string().email().meta({ title: 'Login email' })
+// => {
+//   type: 'string',
+//   format: 'email',
+//   title: 'Login email'
+// }
+```
+
+## Custom rules
+
+You can pass a `toJSONSchema` option when creating [custom rules](../extend/custom_rules.md) to modify the computed JSON schema.
+
+```ts
+const lowercaseRule = vine.createRule(
+  (value, _, field) => {
+    if (!value.match(/[a-z]/)) {
+      field.report('The {{ field }} field can only contain lowercase letters', 'lowercase', field)
+    }
+  },
+  {
+    toJSONSchema(schema) {
+      schema.regex = '/[a-z]/'
+    }
+  }
+)
+
+vine.string().use(lowercaseRule())
+// => {
+//   type: 'string',
+//   regex: '/[a-z]/',
+// }
+```